1. Field of the Invention
The present invention relates to a semiconductor light emitting device and a manufacturing method thereof, and more specifically to a structure capable of preventing end face damage in semiconductor light emitting devices.
2. Description of the Related Art
Many surface states are present on a resonator end face of a semiconductor laser obtained by cleavage, and the temperature is increased by non-emission recombination of carriers. Consequently, the temperature of a portion adjacent to the end face becomes higher than that of the inner portion of the resonator, causing reduction of the band gap adjacent to the end face and self absorption of laser light. As the result, a positive feedback in temperature occurs in which the temperature is further increased. In the end, the temperature of the end face reaches the melting point of the material, leading to physical destruction and laser output degradation, which is known as COMD (Catastrophic Optical Mirror Damage). As for the methods of preventing such end face destruction, the following are generally known: (1) A method of using a structure (window structure) that prevents self absorption of laser light by increasing the band gap energy adjacent to the end face and (2) a method of decreasing peak optical density of the active layer by increasing the beam spot diameter of laser.
One of the specific methods of the type (1) described above is proposed as described, for example, in Japanese Unexamined Patent Publication No. 2000-031596 in which a window structure is formed by etching the upper clad layer to the vicinity of the quantum well active layer adjacent to the emission end face and forming a regrowth layer doped with the same dopant as that of the upper clad layer to diffuse the dopant into the quantum well layer and crystallize.
Another method is proposed as described, for example, in U.S. Pat. Nos. 6,541,291 and 6,859,478 in which a window structure is formed by removing the active layer including quantum wells adjacent to the emission end face and filling a material therein having a greater band gap than the quantum well layer, and further diffusing a dopant into the quantum well active layer.
In the mean time, one of the specific methods of the type (2) described above is to increase the beam spot diameter of laser by employing a broad area structure in which the emission region is broadened in the parallel direction with respect to the p-n junction face, and a broad guide structure in which the emission region is broadened in the orthogonal direction with respect to the p-n junction face. The broad area structure is a structure in which the width of current injection stripe is broadened, which is generally known as a method for increasing the output power of a semiconductor laser. In the broad guide structure, the beam spot diameter is increased by increasing the thickness of the light guide layer in SCH structure. In either case, peak optical density of the active layer is decreased by increasing the light spot diameter of laser.
The window structure described in Japanese Unexamined Patent Publication No. 2000-031596, however, poses a problem that reproducibility of device characteristics is poor, since it uses thermal diffusion. The window structure described in U.S. Pat. Nos. 6,541,291 and 6,859,478 poses a problem that device characteristics are degraded, since a portion of the quantum well layer needs to be removed.
In the mean time, in the broad area structure of the type (2), the increased stripe width causes transverse higher order mode oscillation and filament oscillation to be more likely to occur, which poses a problem that uniform oscillation over the entire region is difficult. In the case of broad guide structure, a change in the light guide layer causes the beam profile (NFP, FFP) to be changed and the current threshold value, slope efficiency, and the like are influenced greatly by this, which poses a problem of limiting design flexibility.
In view of the circumstances described above, it is an object of the present invention to provide a semiconductor light emitting device capable of high output operation with high reliability. It is a further object of the present invention to provide a manufacturing method of semiconductor light emitting device having high reproducibility.